This invention relates, in general, to plasma etching of semiconductor substrates, and more particularly to plasma etching of III-V and related materials.
Etching of metals and metalloids has been accomplished for some time by using halogen based plasma chemistries, and more specifically chlorine and fluorine based plasma chemistries have been used. Metalloids are elements in the Periodic Chart found in groups III and V that have been combined to form compounds, or alloys with properties intermediate to those of typical metals and nonmetals, called semimetal or metalloids. Chlorine based plasma chemistries have been preferred to etch these III-V materials. Even though the use of chlorine based chemistries has been somewhat successful at etching these materials, there are still many difficult problems.
For example, chlorine chemistries corrode interconnect lines that are used to route information from one transistor or semiconductor device to another. Interconnect lines are usually formed by metals that are composed of aluminum, an aluminum alloy, or the like. During the etching of these interconnects a trace amount of residual chlorine may be left on the metal lines and surrounding areas. When the etching process is complete and the interconnect lines which are built on a semiconductor substrate are removed from the plasma etch chemistry, the residual chlorine that is left on the substrate is then free to react with the environment. The environment generally has some amount of moisture or humidity which will react with the residual chlorine to produce hydrochloric acid. The hydrochloric acid then continues to indiscriminately etch the metal interconnect lines. This etching process continues until either chlorine, moisture or metal is exhausted.
Many processes have been developed to help reduce levels of residual chlorine left on the semiconductor device after plasma etching. While these processes have had some beneficial effects in reducing corrosion. They have not, however, resolved the problem totally.
Metals and III-V materials have always been difficult to etch. Etching of III-V materials have been commonly achieved in chlorine based plasma chemistries as written about by E. L. Hu and R. E. Howard, "Reactive-Ion etching of GaAs and InP using CCl.sub.2 F.sub.2 /Ar/O.sub.2 ", Applied Physics Letters, 37(11), page 1022 (1980). Etching of metals and III-V materials is usually achieved in chlorine based plasma chemistries which commonly use low pressure and high physical bombardment levels to achieve removal of material. It has been know for a long time that etch products of metals and III-V materials with the use of chlorine based chemistries have a low volatility. This low volatility of etch products has caused problems in etching of these materials such as slow etch rates, residual material, inadequate masking structures, or the like.
Etching metal and metalloids in a plasma composed of methane (CH.sub.4) and hydrogen (H.sub.2) specifically for III-V semiconductor materials was first demonstrated by U. Niggebrugge, et. al., "GaAs and Related Compounds", Inst. Phys. Conf. Ser. No 79, Karuizawa, Japan, (1985) pp. 367-372. The use of methane and hydrogen chemistries for etching III-V materials has been shown to be feasible, but problems still persist such as low etch rates, due to competing plasma enhancement chemical vapor deposition, and etch initiation is being slow.
It can be seen that conventional plasma etch processing techniques involving chlorine chemistries are not adequate for etching III-V metalloids and related materials. Low volatility of etch products retards the etch rates of these materials. Corrosion plays a major role in yield, device performance, packaging, reliability and life times of devices that are manufactured by dry plasma etching. Therefore, a method that would remove corrosion as a problem and increase volatility of etch products would be highly desirable.